The interlock switch assembly of the invention is constructed for use in X-ray systems in order to protect the health and safety of the personnel operating such systems. However, it will become evident as the description proceeds that the switch assembly of the invention has general application for providing an effective electrical interlock which operates in conjunction with access doors or ports, and which positively prevents the application of electric power to the equipment when such access doors or ports are opened, even in the event of failure of the power relay in the electrical system.
Although interlock systems have been used in the past, many medical and industrial accidents have occurred in X-ray laboratories, where the interlock systems have failed, and the operators are inadvertently subjected to exposure of X-rays and other harmful radiations and emissions. An important feature of the interlock switch assembly of the present invention is that it assures that the power is cut off from the X-ray machine, or the like, when the access door is opened. Unlike the prior art safety interlock systems, the switch assembly of the present invention assures that power to the equipment will be cut off when the access door is opened, even in the event that the safety interlocks themselves should fail.
The power disconnect feature of the interlock switch assembly of the invention is accomplished, as mentioned briefly above, by means of two microswitches connected in series, and which are respectively actuated by two electrically conductive spring strips which are spaced and insulated from one another. The spring strips are normally biased out of contact with the actuator buttons of the microswitches. However, whenever the door is closed, a short-circuited plunger unit, which is mounted in the door, is moved against the spring strips to move them against the actuator buttons of the microswitches so as to actuate the microswitches.
The short-circuited plunger unit also provides a bridging electrical contact between the spring strips which serves to complete the circuit to the high voltage transformer primary of the X-ray generator. This means that even though the power relay may fail in a conductive condition, the circuit to the X-ray generator high voltage transformer is still broken by the interlock switch assembly of the invention when the door is opened.
Therefore, the circuits associated with the interlock switch assembly of the invention are such that power can be applied to the X-ray machine only when the door is closed, at which time the circuits are closed mechanically and electrically and only then can the machine be activated. Under normal operation, arcing between the plunger and the spring strips is prevented, since the microswitches open the circuit to the power control relay to de-energize that relay prior to the physical breaking of contact between the plunger and the spring strips of the safety interlock switch assembly.
The interlock switch assembly of the invention may have an added safety feature, in that it may include an indicator lamp which becomes energized whenever the power control relay is actuated to a closed condition. If a failure should occur in which the relay is welded in a closed condition, the indicator lamp will remain energized, even though the door is opened, apprising the operator that such failure has occurred.